Arm (anatomy)

“ The tendons of the common extensor muscle of the fingers are seen on the back of the hand, and their mode of distribution on the back of the fingers.
Practical Explanation. The muscles 5, 6, 10, extend the wrist on the fore-arm. The muscle 8 extends the fingers. The muscle 9 extends the little finger. The muscles 13 extend the metacarpal bone of the thumb, and its first phalanx. The muscle 14 extends the last bone of the thumb. The muscles 10, 13, 14, move the hand laterally.
160. Where are the muscles situated that effect the larger movements of the hand? ”

“ In your arm there is not a string, but a body, placed very much as our string is placed, and which has the power of shortening itself when required. Every time it shortens itself it bends the arm, and when it has done shortening and lengthens again, the arm falls back into its straight position. This body which thus can shorten and lengthen itself is called a muscle.{28}
If you put one hand on the front of your other upper arm, about half-way between your shoulder and elbow, and then bend that arm, you will feel something rising up under your hand. ”

“ Several of the muscles in the forearm run into tendons in the wrist because if the muscle part were to extend along the wrist, this part of the arm would be large and clumsy instead of graceful and slender. ”

“ When the arm is broken, if one stretch the fore-arm and adjust it while in this position, the muscle of the arm will be bound while extended; but when the dressing is over, and the patient bends his arm at the elbow, the muscle of the arm will assume a different shape. ”

“ That I had not heard, but the weight of iron and his own body was all curiously pressed upon one forearm, and the pain of it set him groaning like a wounded bull. The strangest thing of all was that this arm was free. ”

“ The wrist or joint between the hand and arm lessens on closing the hand, and grows larger when it opens. The contrary happens in the arm, in the space between the elbow and the hand, on all sides; because in opening the hand the muscles are extended and thinned in the arm, from the elbow to the wrist; but when the hand is shut, the same muscles swell and shorten. The tendons alone start, being stretched by the clenching of the hand. ”

“ For the back stroke therefore, and that the arm may not only bend at the elbow, but also extend and straighten itself with force, other muscles, the longus, and brevis brachiæus externus, and the aconæus, placed on the hinder part of the arms, by their contractile twitch, fetch back the fore-arm into a straight line with the cubit, with no less force than that with which it was bent out. The same thing obtains in all the limbs, and in every moveable part of the body. ”

“ None but an anatomist can duly appreciate the variety of separate actions, on which depend the motions of a single limb, and the consequently numerous opportunities of rest which the muscles enjoy. To the superficial and unscientific observer, an arm is an arm; it is a single member which may be fatigued by a day’s work and recruited by a night’s rest. But to the anatomist the arm is a complex object, and its muscular energy is that of its component muscles, each of which may be fatigued by a minute’s action and recruited by a minute’s repose. ”

“ Besides these peculiarities of the hands and feet, which, moreover, are supplied in every joint with tendons and muscles of great motive power, the fore-arm is capable of turning the wrist forwards or backwards, or, as it [Pg 213] is called, rotating, and also of bending. Again, the upper arm is loosely but firmly attached to the shoulders and neck, so as to admit of great range of motion, so what with the bending and rotation of the fore-arm, and the mobility and cushioned state of the fingers, these creatures possess a wonderful apparatus, suited for extreme action and safe holding on. ”

“ In this upper-arm type the muscles affected are supplied by three different nerve-stems—the axillary, musculo-cutaneous, and the radial. In the forearm type the most common variety consists in paralysis of the extensors of the wrist, thus exactly imitating lead palsy.44 The supinator remains intact, the intrinsic muscles of the hand are sometimes intact, sometimes paralyzed. ”

“ Our first thought is to suppose that a long forearm, being a weak lever, will be ill adapted for climbing. But when you look at Fig. 10, the explanation becomes plain. When a branch is seized by the hand, and the whole weight of the body is supported from it, the entire machinery of the arm changes its action. The forearm is no longer the lever which the brachial muscle moves (Fig. 10) , but now becomes the base from which it acts. The part which was its piston cord now serves as its base of fixation, and what was its base of fixation to the humerus becomes its piston cord. ”

“ The muscle, directly that “something” comes to it along its nerves, contracts, shortens, and grows thick; it rises up in the arm; its lower tendon pulls at the radius; the radius with the ulna moves on the fulcrum of the humerus at the elbow-joint, and the arm is bent. ”

“ The arm is either allowed to rest upon the table, upon the flexor mass of muscles of the forearm near the elbow as a kind of movable fulcrum, or is held with the forearm parallel to the table and a short distance above it. ”

“ I have the power to move my arm—by my will to make potential manifestations through this arm. If, however, by any means, you break any of the links out of the chain which unites the divine in me, through my spirit, with the matter of my arm—abstract the electricity, the magnetism, or nerve-force—I lose all power over my arm. Bisect the motor-nerve, which connects my arm with my brain, and my arm will hang lifeless by my side. ”

“ In cases where obstruction to the arterial circulation is more general, so that it requires an increased heart-force to pump the blood through its channels, we observe the heart itself to become larger, and thus its increase of structure (like the blacksmith's arm) is adapted to the required increase of function. The head of the thigh-bone, when irreducibly dislocated, becomes surrounded in its new position with fibro-ligamentous and muscular structures, which so far resemble an articulation as to permit the patient to walk about. ”

“ The arm as a whole would grow neither pale nor cold, it would not become clumsy or heavy, you would not lose your feeling in it, but nevertheless if you tried to bend your arm you would find you could not do it. You could not make the biceps contract, though all the rest of the arm might seem to be quite right.
What does this teach us? It teaches us that the power which a muscle has of contracting when called upon to do so, may be lost and regained, and that it is lost when the blood is prevented from getting to it. When a cord is tied round the whole arm, the power of the whole arm is lost. ”

“ Perfect freedom of movement is insured by the bones being covered with glistening cartilages, and a delicate and moist membrane, and the motion from the shape of the apparatus is almost equal to that of a chandelier where there is what is called a cup-and-ball joint at the ceiling. It has already been noticed that muscles are attached to the blade-bone and to the arm-bone below the joint, and that, this being movable, when they contract they move the arm, and the instance was given of the action of the deltoid muscle in raising the arm. ”

“ And so I managed to do my duty and satisfy my curiosity at the same time. The torso was slight and deformed; the right arm attenuated,—the left full, round, and of perfect symmetry. It had run away with the life of the other limbs,—a common trick enough of Nature's, as I told you before. If you see a man with legs withered from childhood, keep out of the way of his arms, if you have a quarrel with him. He has the strength of four limbs in two; and if he strikes you, it is an arm-blow plus a kick administered from the shoulder instead of the haunch, where it should have started from. ”

“ Why does the muscle contract when that something reaches it? We must be content to say that it is the property of the muscle. But it does not always possess this property. Suppose you were to tie a cord very tightly around the top of the arm close to the shoulder. If you tied it tight enough the arm would become pale, and would very soon begin to grow cold. ”

“ Every limb shrinks sensibly in volume from this withdrawal of the blood, and the shrinkage of any one of them, say the right arm, is measured by the fall of water in a gauge that communicates with a long bottleful of water, through the neck of which the arm has been thrust, and in which it is softly but effectually plugged. ”

“ A fourth muscle exists, which veterinary anatomists include in the study of the three portions of the triceps which we have just been discussing, in giving it the name of small extensor of the forearm. But, as this muscle is no other than the anconeus, and as, in human anatomy, we describe the latter, according to custom, in connection with the forearm, it is when on the subject of the latter that we will concern ourselves with it. ”

“ This gives the muscle greater play than in us, and enables it to lift, more slowly perhaps, but more efficiently, for the arm-bone between the joint and the place where the muscle is attached, is the long arm of a lever which is shorter in man. Below the globular head of the arm-bone is the shaft or cylindrical part of the bone which gives origin to the three-headed muscle called triceps, and is covered by the two-headed one (biceps) already mentioned, besides the deltoid. ”

“ Here are eight arms about three inches in length, united at their roots, and placed circularly at equal distances in the same plane, which has a considerable sinking towards the center. These arms diminish from their rise to their extremities, and end exceedingly small. Near the head they are quadrilateral, but the under-side contracting gradually to an edge, they become towards the ends trilateral. On the upper side of each arm are two rows of acetabula, or suckers, standing in a beautiful order, as close as they can well be placed, and beginning from the center of all the arms. ”

“ The bones of the arm were strong, with strong projections for the attachment of muscles; those of the wrist were few in number and closely united. The rudimentary first finger, or thumb, consisting of a single slender bone, was turned backward toward the shoulder for the support of the membrane in front of the elbow. ”

“ Now see why it is that these large muscles are put so far away from where they do their work. If they were put in the hand, they would make it a large and clumsy thing. They are therefore put up in the arm, where there is room for them, and they have small, but very strong cords by which they pull the fingers. They give to the arm that round fullness that makes its shape so beautiful. ”

“ Again, it is the arm, forearm, or hand that moves in various ways, and to different ends; sometimes there is a combination of movements, like those required for swimming or prehension; the fingers may lock together with force, as if to retain an object, or extend themselves with a lively movement, as if to scatter something. It is probable that, if our instruments were more perfect, we should find in each center a number of subordinate centers for the execution of single movements, or the moving of a single muscle. ”

“ But what makes the muscle contract? You willed to move your arm, and moved it by making the muscle contract; but how did your will accomplish this? If you should examine, you would find running through the muscle soft white threads, or cords, which you have already learned to recognize as nerves. These nerves seem to grow into and be lost in the muscle. If you trace them in the other direction you would find that they soon join with other similar nerves, and the several cords joining together form stouter nerve-cords. ”

“ As for the arms, it is noticeable that they still retain the ordinary mammalian habit in being hairier on the back than on the front; and this also is quite in accordance with our present suggestion, because the same differentiating causes have not worked upon the arm as they work upon the back and legs. The peculiar position of the anterior extremities in man, together with the erect posture, makes the arms come much more frequently into frictional contact with the body or clothing on their inner than on their outer surface. ”

“ Your arm must be raised until high overhead, the hand hanging from the wrist and dropped into your lap or down at the side, letting the elbow "give," so that the upper arm drops first, and then the fore arm and hand,—like three heavy sand-bags sewed together. The arm can be brought up to the level of the shoulder, and then round in front and dropped. ”

“ We can feel that the arm is moving, and, at this instant it is moving backward, for our own experience when we walk and swing our arms naturally is that each arm goes back as the leg on that side goes forward. The man’s arm will reach its furthest point backward when he brings his full weight on the right foot. In a word, the poise of the arm and the poise of the leg correspond.{103} They present an example of repetition of balance. It is enforced, you will observe, in the composition by the arm being made parallel to the direction of the backward leg. ”

“ A series of horizontal metal arms, tipped with celluloid, slide easily through holes in the vertical wooden arm. These metal arms are shaken out to their full length, and their ends pushed rapidly and lightly against the subject's back in the median line, the point of the uppermost horizontal arm being applied to the seventh cervical vertebra. ”